Taking Proper Care of your Turbo-Charged Engine
If you are new to high altitude flying and turbo-charged engines, you will want to spend time getting to know how to take care of your engine. This is essential. It is different up in the flight levels. You can not treat your turbo like a normally aspirated engine, with quick throttle changes. Turbo-chargers are expensive, too. The turbo-charger assembly, including the turbine, the compressor and the connecting shaft will turn at speeds ranging from 50,000 RPM at the low end, to over 100,000 RPM, at cruise. It gets very hot in there and it depends on oil for both lubrication and cooling. Shock cooling is now a major concern. This requires advance planning for descents, and the ‘one inch of manifold-pressure-per-minute-power-reductions’ is a generally accepted rule of thumb for turbo-charged engines. You can not just pull the power back and start down like you might have done before, unless you have to make an emergency descent. The waste-gate operation is either fixed, manually adjusted or automatic. You will want to consult the POH for the airplane you will fly.
You will now find power settings where ‘over square’, such as 30/19 is the rule and not the exception, especially if is a geared engine, such as on the CE 421. In the CE 421, the engine turns faster than the propeller and has a reduction gear box, for better efficiency and developing higher horsepower. Since your engine can now deliver sea level horsepower to a much higher altitude, you will not be losing an inch per 1000’ on climb out as you did before in your normally aspirated engine. But now you will have to monitor engine temperatures more carefully during climb-out. You might also have cowl flaps, which help to manage engine temperatures, by drawing more air in through the engine compartment for better cooling, and out through the cowl flap, when open, for takeoff and climb.